Asian wild rice no longer ‘wild’

The genetic diversity of Asian wild rice (Oryza rufipogon) has been eroded by admixing with domesticated rice strains, researchers said in a new report, a development that may have a negative impact on production of hybrid rice varieties.

Asian wild rice is believed to be a descendant of the wild ancestor of the first Asian domesticated rice 8,000 years ago, and is an important component of the primary gene pool used in modern rice breeding.

The main value of wild rice genes comes from disease-resistant traits the variety naturally has, the research team explained. Diseases such as grassy stunt and Tungro have been successfully eliminated from most domesticated rice as a result of using wild rice genes in breeding programs, for example.

The researchers led by Professor Chu Chengcai of the Institute of Genetics and Developmental Biology,
Chinese Academy of Sciences, together with scientists from the University of Copenhagen and the University of California at Berkeley found, however, that the genetic variation of Asian wild rice has been heavily eroded by extensive gene flow from domesticated rice.

“Asian wild rice is a hybrid swarm, co-evolves and is connected to domesticated rice by continuous and extensive gene flow,” said study first author Dr. Wang Hongru. “The insight that most Asian wild rice is heavily admixed, and that some may even be feral rice, has great impact on rice domestication research.”

The study explained that it is common practice to use the geographic distribution and genetic variation of wild relatives to pinpoint origin of domestication for crops, and that many previous rice domestication studies also relied on the assumption that Asian wild rice is ‘pure’ descendants of ancestral populations that gave rise to domesticated rice. The study’s results, however, now cast doubt on the earlier research, which could have implications for developing suitable varieties for different areas.

“We should be cautious when evaluating the results of these studies,” Wang said.
The study was published in the latest issue of Genome Research.